A common problem associated with construction that involves the clearing, grading, and leveling of land is the subsequent erosion of the resulting bare soil by rainwater and consequent pollution of rivers and streams by silt carried from the land with the rainwater. The problem has become so acute in some areas that regulations have been imposed upon developers requiring that silt barriers be erected to trap and contain silt that might otherwise be washed from the construction site into adjacent streams. In addition, surprisingly large volumes of silt can be washed from newly graded land such that additional soil must sometimes be brought in to replace the silt that was washed away.
One prior method of controlling silt erosion has been to erect silt barriers or fences on graded land in the path of running rainwater. Such barriers are sometimes formed from sheets of porous material called silt cloth mounted to upstanding wooden stakes. The silt cloth is adapted to pass water and to prevent passage of silt so that running water encountering the barrier passes through the cloth while silt suspended in the water is trapped behind the cloth.
Problems with these types of silt barriers have been numerous. For example, the barriers are generally flimsy and are often erected improperly such that they are easily uprooted by the force of running rainwater, thus allowing continued erosion of the land. Further, since water does not always drain from land along a single or well defined path, it can be difficult to determine the proper locations to erect the barriers. Consequently, barriers typically are erected across all potential drainage paths, which is expensive and time consuming. As a consequence, these types of silt barriers can be an ineffective and expensive method of controlling silt erosion. Also, since the barriers function as simple filters, they tend to become clogged and inefficient over time.
Another method of controlling silt erosion has been to construct a silt collecting pond at a lower elevation on land subject to erosion. An elongated cylindrical stand pipe is commonly placed in a vertical orientation within the pond and V-shaped weirs are formed around the top of the pipe. A drainage pipe in communication with the standpipe at its bottom portion extends outside the silt collecting pond. With this method, rainwater flows from higher elevations of the land and fills the silt collecting pond until the water level in the pond rises to the bottom of the V-shaped weirs. Excess water then drains through the weirs into the standpipe and out of the pond through the drainage pipe. the weirs into the standpipe and out of the pond through the drainage pipe.
With the just described method, water normally stands in the pond at or below the level of the weirs so that silt can precipitate to and collect on the bottom of the pond. Problems with this method have been that water standing in the pond tends to attract mosquitoes, algae, and, in general, forms an unsightly and unhealthy quagmire. Further, sticks and other debris tend to get caught in the weirs preventing proper drainage of water therethrough and consequently decreasing the efficiency and effectiveness of the device.
A common problem with both silt fences and collecting ponds arises when they are used along an extended sloped grade where a plurality of barriers or collecting ponds are positioned at intervals along the grade. In these situations, flowing water accumulates as it flows past each successive barrier such that at the bottom of the slope the flow can become a torrent that washes away even the best silt fences and collecting ponds. Prior art control methods have therefore proven ineffective for use on such extended slopes.
Finally, with prior art methods the silt fences and stand pipes must generally be removed and discarded after the land on which they were installed has been graded, leveled, and stabilized. In many cases, separate drainage systems must subsequently be installed to insure adequate drainage of rainwater from the land in the future.
There is, therefore, a persistent and heretofore unaddressed need for a method and apparatus for controlling silt erosion that overcomes the many problems associated with prior art silt control methodologies. It is to the provision of such a method and apparatus that the present invention is primarily directed.